LK-99

LK-99 is a gray to purple polycrystalline compound, a copper doped lead oxyapatite first studied as a candidate superconductor in 1999 by a team at Korea University led by Lee Sukbae and Kim Ji-Hoon. The material drew worldwide attention in July 2023 when the team posted preprints claiming it acted as a superconductor at room temperature and ambient pressure, at temperatures up to 400 kelvin. Laboratories around the world moved quickly to reproduce the result, and within weeks a scientific consensus formed that LK-99 is not a room temperature superconductor and is in fact an insulator in its pure form, with several replication attempts tracing the misleading signals to a copper sulfide impurity that can mimic superconducting behavior in small samples. One of the original authors, Lee, said afterward that the preprints had been incomplete, and coauthor Kim Hyun-Tak said one of the papers contained flaws.